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New 6th Street Bridge, L.A., USA

 
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Dr. N. Subramanian
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PostPosted: Wed Feb 03, 2016 4:49 am    Post subject: New 6th Street Bridge, L.A., USA Reply with quote

New 6th Street Bridge, L.A., USA
The following photo shows the 6th street Viaduct in L.A., USA. Also known as the Sixth Street Bridge, it is an important engineering landmark in the City of Los Angeles.  It is one of a set of fourteen historic Los Angeles River crossing structures, and is the longest of these structures, with a span of 3500 feet. The bridge has appeared in numerous films, television shows, music videos and video games since 1932, including Terminator 2 & 3, and Furious 7.

It has a 46 foot wide, four-lane roadway with 11-foot eastbound and westbound inside traffic lanes and 12-foot outside lanes with no shoulders.  There are sidewalks of varying widths on both sides.

The Sixth Street Viaduct was constructed using then state-of-the-art concrete technology and an onsite mixing plant.  However, just 20 years after the Sixth Street Viaduct was constructed, its concrete supports began to disintegrate due to a chemical reaction known as Alkai Silica Reaction (ASR), causing significant deterioration of the structure.


A 2004 study found itís susceptible to collapse during an earthquake. Despite years of research and consultation with experts worldwide, the Conservancy and others could not find a way to halt or reverse the alkali-silica reaction (ASR) that is slowly destroying the bridge.  Over the years, various costly restorative methods have been tried, but none have worked to correct the problem. In addition to its vulnerability to collapse under predictable seismic forces, the Sixth Street Viaduct also has geometric design and safety deficiencies. Hence, the City Council in 2000 decided to replace the bridge.

Hence starting from 7th Feb 2016 the bridge is going to be demolished.  An estimated 48,000 cubic yards of concrete, 1,245 tons of structural steel and 4,200 tons of rebar will be hauled away as construction begins on the replacement.

The new bridge designed by architect Michael Maltzan and the HNTB Design-Build team is set to be completed in 2019. It will take nine months to demolish the existing bridge.


Working alongside engineers HNTB, Architect Maltzan developed a design which accommodates a range of transport facilities. Now, the new viaduct incorporates significant new bicycle connections, and also increases connectivity for pedestrian access, not only at its endpoints, but also along the entire structure.


The new 3,500 foot viaduct is defined by ten pairs of repeated concrete arches, rising and falling along the north and south edges of the bridge as it extends from east to west. Ten arches rise and fall on either side of the roadway. Four of the arches will rise 60 feet. Most will top out at 30 feet. To keep the roadway from feeling hemmed in, each arch slants outward nine degrees, like the spikes on a stegosaurus.

Staircases and bicycle ramps allow pedestrians and cyclists to move throughout the bridge to catch views of the city's skyline to the west and explore the river below.

Four lanes are devoted to cars. The sidewalks vary in width from eight to 14 feet, and the bike lane is 14 feet wide.

the arches incline outward from a deck, which is suspended from the cable lattice at its perimeter.The structureís generous spans create large open spaces below that could form recreational green areas.


The Architect's vision is supported by structural design, created in part by Ted Zoli, an HNTB engineer and a recipient of a MacArthur "Genius Grant."

Maltzan's squiggle design allowed Zoli to support the road with a system of crossed suspension cables within each concrete arch.

This style allows for a thinner roadbed than a bridge with a single tower and a series of cables fanning out from it and gives the undercroft a more inviting disposition, Zoli said.


References:

  • http://www.sixthstreetviaduct.org/faq
  • http://www.designboom.com/architecture/michael-maltzan-los-angeles-sixth-street-viaduct-ribbon-of-light-bridge-02-01-2016/
  • http://www.latimes.com/local/california/la-me-sixth-street-bridge-20150601-story.html
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